Copilot commented on code in PR #2341:
URL: https://github.com/apache/age/pull/2341#discussion_r2897209721
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src/backend/parser/cypher_clause.c:
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@@ -6583,6 +6605,59 @@ static bool clause_chain_has_dml(cypher_clause *clause)
return false;
}
+/*
+ * Build a false WHERE clause that forces a MATCH to return zero rows.
+ * Used when the MATCH pattern references a label that does not exist.
+ *
+ * When volatile_needed is false, returns a constant (true = false) that
+ * PG's planner may constant-fold — this is fine when there is no DML
Review Comment:
These comments introduce non-ASCII em dashes (—). This repo’s C sources
otherwise appear to be ASCII-only, and non-ASCII punctuation can cause
encoding/tooling issues in some build environments. Consider replacing these
with plain '-' or '--' throughout the new comments.
```suggestion
* PG's planner may constant-fold -- this is fine when there is no DML
```
##########
src/backend/parser/cypher_clause.c:
##########
@@ -2949,6 +2952,25 @@ static Query
*transform_cypher_match_pattern(cypher_parsestate *cpstate,
*/
pnsi = get_namespace_item(pstate, rte);
query->targetList = expandNSItemAttrs(pstate, pnsi, 0, true, -1);
+
+ /*
+ * Now that the predecessor chain is fully transformed and
+ * any CREATE-generated labels exist in the cache, check
+ * whether the MATCH pattern references valid labels. This
+ * deferred check is only needed when the chain has DML,
+ * since labels created by CREATE are not in the cache at
+ * the time of the early check in transform_cypher_match().
+ *
+ * We use a volatile false predicate (random() IS NULL)
+ * instead of a constant one (true = false) because PG's
+ * planner can constant-fold the latter into a One-Time
+ * Filter: false, eliminating the entire plan subtree —
+ * including the DML predecessor scan — without executing it.
Review Comment:
The PR description says the deferred invalid-label path injects
`makeBoolConst(false, false)`, but the implementation uses a volatile predicate
(`random() IS NULL`) to avoid constant-fold plan elimination. Please update the
PR description to match the actual approach so future readers don’t
implement/debug the wrong behavior.
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